Apparatus for regulating the transport flow of a liquid that is circulated by a centrifugal pump in a closed pipe system

ABSTRACT

In a closed pipe system, the apparatus regulates the transport flow of a liquid that is circulated by a centrifugal pump. The pump has a characteristic curve that falls in the direction toward zero transport flow from a design point. That is, as the volumetric flow decreases, the pump head increases.

FIELD OF THE INVENTION

The invention relates to an apparatus which regulates the flow through acentrifugal pump used in a closed pipe system.

BACKGROUND OF THE INVENTION

In closed pipe systems, for example heating systems, the demand of theloads connected to the pipe system determines the variable throughflowresistance of the entire system. The loads in a heating system are itsheating bodies, where the valves of these heating bodies adapt to theparticular heat demand and cause a greater or lesser throughflowresistance.

Since the circulation systems addressed here must be designed formaximum transport flow, but often operate only under partial load, therelationship between the required transport pressure and the transportflow of the centrifugal pump has a characteristic which falls in thedirection of zero transport flow. However, the centrifugal pumps whichup to now have been used in such circulatory systems have acharacteristic which rises in the direction of zero transport flow. Thatis, the pump head increases as the volumetric flow rate decreases.

If one wished to operate such a centrifugal pump in the system with asteady rpm, the difference between the pressure created by the pump andthe specific required pressure had to be throttled out, resulting in asubstantial energy loss.

Various regulation systems have already been developed for heatingsystems to obtain a convenient and economical adaptation to demand. Theso-called bypass control is known as a mechanical solution. In a bypasscontrol, a portion of the transport flow is withdrawn by a feedback lineof the pressure side of the pump and is again returned to the suctionside. This measure does indeed reduce the useful transport flow of thesystem, but the system characteristic does not shift towards largertransport flows.

At the present time, regulation systems have established themselveswhich control the rpm of the centrifugal pump so as thereby to achievebroad adaption to various control variables, such as the differencepressure, and the external, inflow, or backflow temperature. Thisregulation is accomplished either by switching to various prescribedrpms, or, with the correspondingly higher complication continuouslyvarying the rpms. What is true about this rpm regulation in general isthat it has small losses compared to the devices described above forregulating the transport flow. However, such a regulatory system is notentirely without losses. Incidentally, with such a regulation too, partsof the pressure difference also must be throttled out.

SUMMARY OF THE INVENTION

It is an object of the present invention to create an apparatus whichrequires little technical complication, which avoids significant losses,and which adapts to changes of the operating state which occur in asystem.

According to the present invention, the object of the present inventionis achieved by use of a centrifugal pump whose pump characteristic fallsin the direction of zero transport flow.

For the inventive apparatus, a pump characteristic is thus proposedwhose pumping head at zero transport flow amounts to about 80% of thepumping head at the design point of the centrifugal pump. Especiallywith heating systems, use of this type of pump provides especially goodadaptation to the operating conditions existing there in heatingsystems.

A pump characteristic which falls in the direction of zero transportflow can advantageously be realized with a centrifugal pump whoseimpeller blades have a blade exit angle of 60° or more, preferably 90°.It should be noted that such an impeller, up to now, has not been usual.

Another supporting factor to achieve a falling pump characteristic is alarge number of blades, for example 11 or more. The blade exit angle andthe number of blades are mutually related, so that the blade exit anglecan be reduced as the number of blades is increased.

Still another supporting factor for achieving a falling pumpcharacteristic is for the impeller to have entry edges which are onlyslightly inclined relative to the rotation axis of the centrifugal pump.Finally, it is also proposed that the approach edge in the transitionregion between a collection chamber following the impeller and the entryinto the pressure connection piece be designed with a sharp edge andwith a right angle. This measure, too, helps to reduce the pumpcharacteristic in the region of the zero transport point.

It is advantageous for the electric motor that drives the centrifugalpump to have a stiff characteristic, so that a change of torque willcause only a slight change of the rotational speed. This feature limitsto a tolerable minimum the undesirable rise of the pump characteristictowards smaller transport amounts, which is caused by the electricmotor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a transport flow/pumping head diagram of a heating systemaccording to the present invention.

FIG. 2 shows an impeller, with the cover plate removed, according to thepresent invention.

FIG. 3 shows a centrifugal pump inlet and outlet according to thepresent invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Referring now to FIG. 1, the abscissa of this diagram is scaled for thetransport flow Q in m³ /h, the ordinate specifies the pumping head H inm. A characteristic (1) of a pump is shown here refers to a circulationpump for a heating system. The pump characteristic for this pump isbell-shaped. The pump's design point (2) is the intersection point ofthe pump characteristic curve (1) with a system characteristic curve(3). The design point is situated about at its maximum, but it can alsolie in the section which drops off towards Q=0. For pump operation, andalso for the regulation apparatus, only that part of the pumpcharacteristic (1) is used which lies between the design point (2) andthe transport flow Q=0.

The heating system can be throttled, e.g., by the activation of a valveon a heating body. This results in a steeper system characteristic (4),which will have a new intersection point (5) with the falling pumpcharacteristic (1). This new operating point (5) has lower pumping headsand transport quantities. Further throttling results in a steeper systemcharacteristic (6), so that the pump operating point (7) has still loweroutput.

The lines and points discussed up to now represent a theoretical basis.The actual demand points (8), occurring in an actual system, woulddiffer slightly from this.

Automatic adaption is actually achieved, without the need forcomplicated regulation having mechanical and/or electronic componentsthat may be susceptible to interference. This results solely fromoperating with the falling pump characteristic curve which correspondsto the operating states that prevail in a closed pipeline system withvariable throughflow resistances.

FIGS. 2 and 3 illustrate a centrifugal pump having a characteristiccurve described above. The pump includes an impeller 11 having blades12. The blades 12 have an entry edge 16 (see FIG. 2). A collectionchamber 13 is disposed downstream of the impeller 11. The pump housinghas a tongue 14 disposed in a transition region between the collectionchamber 13 and an outlet of the pump into an entry of a pressureconnection piece 15. The tongue 14 has a sharp edge having a right angleon a side facing the impeller 11 and has a rounded edge on a side facingthe pressure connection piece 15.

I claim:
 1. An apparatus for regulating the transport flow of a liquidthat is circulated in a closed pipe system by a centrifugal pump toregulate the circulation of water in a heating system comprising acentrifugal pump having a pump characteristic curve that falls in thedirection toward zero transport flow from a design point.
 2. Theapparatus of claim 1, wherein the pump characteristic curve has apumping head at a transport flow of approximately 80% of the pumpinghead at the design point of the centrifugal pump.
 3. The apparatus ofclaim 1, wherein the centrifugal pump has impeller blades that have ablade exit angle of at least 60 degrees.
 4. The apparatus of claim 3,wherein the blade exit angle is about 90 degrees.
 5. The apparatus ofclaim 1, wherein the centrifugal pump has an impeller having at least 11blades.
 6. The apparatus of claim 1, wherein the centrifugal pump has animpeller having entry edges which are only slightly inclined relative tothe rotation axis of the centrifugal pump.
 7. The apparatus of claim 1,wherein the centrifugal pump has a housing having a tongue disposed in atransition region between a collection chamber downstream of an impellerand an outlet of the pump into an entry of a pressure connection piece,said tongue has a sharp edge having a right angle on a side facing theimpeller and has a rounded edge on a side facing the pressure connectionpiece.
 8. The apparatus of claim 1 further comprising an electric motorthat drives the centrifugal pump, said electric motor having acharacteristic such that a change of torque causes only a minimal changeof rotational speed.
 9. The apparatus of claim 1, wherein the pumpcharacteristic curve falls to zero transport flow from the design point.